Sahih Muslim Book 1, Hadith Number 226.

Chapter : The veracity of Faith and its sincerity.

It is narrated on the authority of ‘Abdullah (b. Mas’ud) that when this verse was revealed: “It is those who believe and confound not their belief with wrongdoing” (vi. 82), the Companions of the Messenger of Allah wore greatly perturbed. They said: Who amongst us (is so fortunate) that he does not wrong himself? Upon this the Messenger of Allah (may peace be upon him) remarked: It does not mean that which you presume It implies that which Luqman said to his son: O my son, do not associate anything with Allah, for indeed it is the gravest wrongdoing (xxxi. 13).